1. Field of the Invention
The present invention relates to an improved process for the manufacture of vinyl chloride polymer by means of suspension polymerization.
2. Description of the Prior Art
Various efforts have been made in recent years to reduce the amount of undesired polymer scale formation inside the reactor during the manufacture of vinyl chloride polymer. The formation of such polymer scale, for example, necessitates cleaning of the reactor during batch polymerization operations and is undesirable due to reactor downtime, labor time, and costs in accomplishing the cleaning operation.
Organotin mercaptides have been suggested for use as additives during the polymerization of vinyl chloride monomer in the past without any realization that such compounds, when used in conjunction with an epoxidized vegetable oil, can be used to reduce the amount of polymer scale formation during the suspension polymerization of vinyl chloride monomer, optionally in the presence of one or more copolymerizable monomer(s). For example, in U.S. Pat. No. 2,575,135 to W. A. Schulze et al., the use of mercaptides as modifying agents during emulsion polymerization reactions is proposed to give gel-free polymers of high molecular weight, of uniform characteristics, and of good processability. Additionally, in U.S. Pat. No. 3,862,066 to W. M. Reiter et al. and in "Participation of Sulfur Compounds in Vinyl and Related Polymerization" by P. Ghosh, pp. 195-227, it is suggested that mercaptides depress the polymerization rate and can be added to the polymerization batch near the intended termination point of the reaction to merely act as a short-stopping agent.